1. Field of the Invention
The present invention relates to a perforating apparatus for forming a large number of fine pores in the peripheral surface of a cylindrical article. More specifically, the present invention relates to a higher-speed apparatus for forming a plurality of fine pores in the peripheral surface of a filter of a filter cigarette by means of a laser pulse beam.
2. Description of the Related Art
Some filter cigarettes have a large number of pores in their peripheral surface. The cigarettes of this type are designed so that a smoker can inhale plenty of air through these pores while smoking, thereby enjoying a soft feeling of smoking. In these cigarettes, moreover, cigarette smoke can be diluted and lowered in temperature and in the contents of harmful ingredients.
Conventionally, an apparatus for perforating a large number of pores in filters of filter cigarettes is disclosed in Published Unexamined Japanese Patent No. 63-139375, 63-294773 (U.S. Pat. No. 4,860,773) by the inventor hereof. This apparatus comprises a rotatable perforating disk, and a plurality of retaining arms are arranged circumferentially on the peripheral edge portion of the disk. These retaining arms hold cigarettes supplied from a preceding process, and rotate around their own axes while moving around and together with the disk. The apparatus further comprises a laser pulse source for generating laser pulses and an optical system. The optical system radially splits a laser pulse beam by means of a beamsplitter, e.g., a conical polygon mirror, and radially applies the resulting split beams from the central portion of the perforating disk to the respective peripheral surfaces of the filters of the cigarettes held by means of the retaining arms.
In the conventional apparatus constructed in this manner, the pulsative laser beams are applied to the peripheral surfaces of the filters of the cigarettes held on the retaining arms as the cigarettes rotate around their own axes, whereby a plurality of fine pores are bored at fine intervals in the peripheral surfaces of the filters. In this apparatus, moreover, all of its principal moving parts, including the perforating disk and the retaining arms, rotate, so that high-speed operation is easy, and the cigarettes can be processed in plenty.
If the apparatus of this type is set in a production line for cigarettes, the number of cigarettes supplied per unit time from a preceding process, such as a cigarette manufacturing apparatus, must naturally be equal to the number of cigarettes processed per unit time in this perforating apparatus. In the cigarette production line, the supply of cigarettes per unit time is very large, so that the operating speed of the apparatus must be made as high as possible.
In this conventional perforating apparatus, each retaining arm is provided with a vacuum chuck mechanism for holding a cigarette, a gear mechanism for rotating the chuck mechanisms around their own axes, etc., and the circumferential intervals of arrangement of the arms cannot be made very short. If the number of cigarettes received per unit time by the retaining arms is made equal to the large number of cigarettes supplied from the preceding process, the circumferential speed of the perforating disk will become extremely high. As a result, a greater centrifugal force acts on the cigarettes held on the retaining arms, so that the arms become unable to retain the cigarettes. Thus, the limit of the operating speed of the conventional apparatus depends on the limit of the circumferential speed of the perforating disk.
Disposed beside the perforating disk, moreover, are supply and delivery mechanisms, such as a supply roller for supplying the cigarettes to the retaining arms, a delivery roller for delivering the cigarettes from the arms, etc. Accordingly, the cigarettes held by means of the retaining arms must finish making at least one revolution around their own axes, thereby accomplishing perforation, before they are discharged by means of the delivery roller after being supplied from the supply roller. If the supply and delivery rollers are situated at an angular distance of 180.degree. with respect to the perforating disk, for example, the cigarettes finish being perforated while being transported between these rollers, that is, while the perforating disk rotates through 180.degree.. Thus, no cigarettes are held on the retaining arms in the remaining 180.degree. range. Meanwhile, the optical system of this apparatus is arranged so that the beamsplitter radially splits and applies the laser beams throughout the circumference, that is, over the range of 360.degree.. In the remaining 180.degree. range, therefore, laser pulses are applied to vacant retaining arms, resulting in a waste of the energy of the laser beams. In the conventional perforating apparatus, therefore, the output of the laser pulse, source must be made high enough to compensate for the energy loss of the laser pulses. In order to increase the operating speed of the apparatus, however, the rotating speed of the perforating disk should be increased, so that the time intervals between the laser pulses must be shortened. Accordingly, the energy of each pulse is reduced, exerting a bad influence on the shape of the resulting pores. Thus, the aforesaid energy loss of the laser pulses is expected to be minimized.